Organic electroluminescent display and method for fabricating the same

ABSTRACT

A method of fabricating an organic electroluminescent display by forming a lower electrode on a substrate and forming an insulating film with an opening part for exposing a portion of the lower electrode. An organic thin film is formed on the substrate and a surface of a portion of the organic thin film layer is selectively treated. A luminescent layer is formed on another portion of the organic thin film layer; and an upper electrode is formed on the front of the substrate.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of KoreanPatent Application No. 2002-67975 filed on Nov. 4, 2002, the disclosureof which is hereby incorporated by reference in its entirety.

BACK GROUD OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an organic electroluminescentdisplay and, more particularly, to an organic polymer electroluminescentdevice capable of preventing leakage current between adjacent pixels andimproving inkjet-printing quality of a luminescent layer by selectivelytreating the surface of a hole transport layer and a method forfabricating the same.

[0004] 2. Description of Related Art

[0005]FIG. 1 illustrates a cross sectional view of one pixel of aconventional organic electroluminescent display.

[0006] Referring to FIG. 1, a buffer layer 110 is formed on aninsulating substrate 100, and a thin film transistor 120 is formed onthe buffer layer 110 in an ordinary manner. As shown in FIG. 1, the thinfilm transistor comprises a gate 125, a source electrode 127, which iselectrically connected to the source region 121, and a drain electrode129 which is electrically connected to the drain region 123.

[0007] A via hole 135 for exposing one of the source electrode 127 orthe drain electrode 129, e.g., the drain electrode 129 is formed on aninsulating film 130 after the insulating film 130 is formed on the thinfilm transistor 120 and the buffer layer 110. A lower electrode 140which is connected to the drain electrode 129, for example, through thevia hole 135 is formed on the insulating film 130. An opening part 155for exposing the lower electrode 140 is formed by patterning aplanarization film 150 after the planarization film 150 is deposited onthe substrate.

[0008] Subsequently, a hole transport layer 160 is formed, for example,by spin coating an organic material such as PEDOT (Poly-3,4-Ethylenedioxythiophene) or PANI (polyaniline) on the substrate. Aluminescent layer 170 is formed on the hole transport layer 160 of theopening part 155 via an inkjet process, and an upper electrode 180 isformed over the substrate.

[0009] Ordinarily, the luminescent layer is formed by using an inkjetprocess or by using laser induced thermal imaging (LITI) process when anorganic polymer material is used as the luminescent layer of the organicelectroluminescent display.

[0010] The inkjet process is a process for forming the luminescent layeron a lower electrode by injecting the solution onto the substrate fromthe inkjet head. The solution is ejected at a high speed from a headcontaining solution comprising EL (electro-luminescence) material, e.g.,organic polymer EL material, such that the solution is arranged whilethe inkjet head is spaced apart from the substrate at a certaindistance.

[0011] Although respective R, G and B luminescent layers should beindependently formed per each pixel in an organic luminescent display,there has been a problem in that a solution comprising organic polymermaterial which is ejected from the head is dispersed onto adjacentpixels in case of the inkjet process.

[0012] In order to solve the problem, it is suggested in Korean PatentApplication No. 10-1999-7010647 that a luminescent layer is formed afterforming a bank layer to cover the edge part of the lower electrode pereach pixel. The bank layer is formed of an insulating material. Themethod for forming a luminescent layer via an inkjet process using thebank layer enables the luminescent layer to be independently formed pereach pixel by preventing a solution comprising an organic polymermaterial from being dispersed onto adjacent other pixels. Thus, by usingthe bank layer the solution is provided only on the upper part of thelower electrode of a relevant pixel.

[0013] However, there has been a problem in that printing quality islowered as a solution comprising an organic polymer material isdispersed on the bank layer since surface characteristics of the holetransport layer are maintained in all the pixels on the substrate byforming a hole transport layer over the substrate after the bank layeris formed, even when the inkjet process uses the bank layer.

[0014] Furthermore, a conventional organic electroluminescent displayforms a hole transport layer 160 that has conductivity between the lowerelectrode 140 and the luminescent layer 170. Thus, luminescenceefficiency is improved by improving injection efficiency of holes fromthe lower electrode 140 to the luminescent layer 170. However, there hasbeen a problem that light is emitted even from adjacent off pixelsbecause the hole transport layer which is conductive is formed over thesubstrate. Thus, leakage current flows between the hole transport layer160, which is conductive and the lower electrode 140.

[0015] There have also been problems in that a process for forming anadditional partition wall is required, and adhesion defects aregenerated between the succeeding cathode electrode and the organicluminescent layer due to the stepped profile of a the thick partitionwall. When the organic luminescent layer is formed using a partitionwall for defining a pixel region on which the organic luminescent layeris to be formed, a thick partition wall should be formed to cover theedge part of a pixel electrode.

SUMMARY OF THE INVENTION

[0016] This invention provides a method of fabricating an organicelectroluminescent display by forming a lower electrode on a substrateand forming an insulating film with an opening part for exposing aportion of the lower electrode. An organic thin film is formed on thesubstrate and a surface of a portion of the organic thin film layer isselectively treated. A luminescent layer is formed on another portion ofthe organic thin film layer; and an upper electrode is formed on thefront of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

[0018]FIG. 1 is a cross sectional view of a conventional organicelectroluminescent display.

[0019]FIGS. 2A, 2B and 2C are cross sectional views for explaining amethod for fabricating an organic electroluminescent display using UVsurface treatment according to exemplary embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will now be described in detail inconnection with exemplary embodiments with reference to the accompanyingdrawings. For reference, like reference characters designatecorresponding parts throughout several views.

[0021]FIGS. 2A, 2B and 2C illustrate cross sectional structures forexplaining a method for fabricating an active matrix organicelectroluminescent display according to exemplary embodiments of thepresent invention.

[0022] Referring to FIG. 2A, a buffer layer 210 is formed on aninsulating substrate 200, and a thin film transistor 220 is formed onthe buffer layer 210. The thin film transistor 220 comprises a sourceregion 212 and a drain region 223 which are formed on an activationlayer. The thin film transistor 220 further comprises a gate 225, asource electrode 227 which is electrically connect to the source region212 and a drain electrode 229, which is electrically connected to thedrain region 223.

[0023] An insulating film 230 is formed over the buffer layer 210 andthe thin film transistor 220. A via hole 235 exposes one of the sourceelectrode 227 or the drain electrode 229, e.g., the drain electrode 229and is formed by etching the insulating film 230. A lower electrode 240,which is connected to the drain electrode 229 through the via hole 235,is formed on the insulating film 230.

[0024] A planarization film 250 is formed by spin coating aplanarization material, such as, acryl on the substrate, and an openingpart 255 is formed by etching the planarization film 250 so that aportion of the lower electrode 240 is exposed. A hole transport layer260 is formed by spin coating a conductive polymer material, such as,PEDOT (Poly-3, 4-Ethylenedioxythiophene) or PANI (polyaniline) on thesubstrate including the opening part 255.

[0025] As shown in FIG. 2B, the surface of the hole transport layer 260is treated by selectively irradiating UV rays 310 onto the holetransport layer 260. The surface of the hole transport layer 260 isselectively treated by irradiating UV rays 310 onto the hole transportlayer 260 while a portion of the hole transport layer 260 correspondingto the lower electrode 240, namely, a portion corresponding to aluminescence region of each pixel is masked using a mask 300. Anun-masked portion 265 of the hole-transport layer 260 where the surfaceis treated by irradiation of UV rays, that is, the non-luminescenceregion of each pixel has hydrophobicity. The masked portion 261 of thehole-transport layer 260 on which UV rays are not irradiated, that is,the luminescence region has hydrophilicity. Therefore, un-masked portion265 of the hole-transport layer 260 where the surface is treated byirradiation of UV rays has surface characteristics which are differentfrom the masked portion 261 of the hole-transport layer 260 on which UVrays are not irradiated. Also, the un-masked portion 265 of thehole-transport layer 260 has a relatively high resistance value comparedwith the masked portion 261 of the hole-transport layer 260 so that theun-masked portion 265 where the surface is treated by irradiation of UVrays is in the nonconductive state.

[0026] Referring to FIG. 2C, a luminescent layer 270 is formed on thehole transport layer 260 via an inkjet process, wherein a solutioncontaining an organic polymer material is dispersed onto the holetransport layer 260. The solution which is ejected from the inkjet headis prevented from dispersing onto neighboring pixels because the surfaceof the un-masked portion 265 of the hole-transport layer whichcorresponds to a non-luminescence region in the hole transport layer 260is treated with UV rays. Thus, the un-masked portion 265 of thehole-transport layer 260 which corresponds to a non-luminescence regionhas surface characteristics different from the masked portion 261 of thehole transport layer 260 which corresponds to a luminescence region overthe lower electrode 240. Therefore, the luminescent layer 270 does notinfluence neighboring pixels and is formed over the upper portion of thelower electrode 240 of a relevant pixel. It is possible for theluminescent layer 270 to only be formed on the upper portion of thelower electrode 240 of a relevant pixel.

[0027] Furthermore, the masked portion 261 of the hole-transport layerwhich corresponds to a luminescence region in the hole transport layer260 maintains the conductive state and is to improve luminescenceefficiency by improving the injection efficiency of holes from the lowerelectrode 240 to the organic luminescent layer 270. The un-maskedportion 265 of the hole-transport layer 260 becomes non-conductive bythe UV surface treatment so that flow of leakage current betweenadjacent pixels via the hole transport layer 260 and the lower electrode240 is prevented.

[0028] A method for fabricating an organic electroluminescent displayusing UV surface treatment of the present invention can not only beapplied to active matrix and passive matrix displays as well asfront-emission luminescent and rear-emission luminescent displays, butcan also be applied to a method for fabricating a flat panel displayusing inkjet process.

[0029] Although exemplary embodiments of the present inventionillustrate methods for UV surface treatment by forming a hole transportlayer on a planarization film, the various embodiments of the presentinvention can also be applied to a method for fabricating an organicelectroluminescent display by forming the hole transport layer andperforming UV surface treatment after forming a bank layer on theplanarization film 250.

[0030] An organic electroluminescent display and a method forfabricating the same according to the present invention prevent alland/or substantially all leakage current between adjacent pixels byirradiating UV rays and treating the surface of a portion of the holetransport layer other than the luminescent region of each pixel. Thus,printing quality is improved when forming a luminescent layer by aninkjet process and the resistance value of a portion on which UV raysare irradiated is increased.

[0031] While the invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method of fabricating an organicelectroluminescent display comprising the steps of: forming a lowerelectrode on a substrate; forming an insulating film with an openingpart for exposing a portion of the lower electrode; forming an organicthin film on the substrate; selectively treating a surface of a portionof the organic thin film layer; forming a luminescent layer on anotherportion of the organic thin film layer; and forming an upper electrodeon a front of the substrate.
 2. The method for fabricating an organicelectroluminescent display according to claim 1, wherein the surface ofthe organic thin film is selectively treated by irradiating the organicthin film layer with UV rays while the another portion is masked.
 3. Themethod for fabricating an organic electroluminescent display accordingto claim 1, wherein the luminescent layer is formed by an inkjetprocess.
 4. The method for fabricating an organic electroluminescentdisplay according to claim 3, wherein the treated surface portion of theorganic thin film layer keeps ink for the luminescent layer within theopening part when forming the luminescent layer by an ink-jet process.5. The method for fabricating an organic electroluminescent displayaccording to claim 1, wherein the insulating film is formed of aninsulating film for planarization.
 6. The method for fabricating anorganic electroluminescent display according to claim 1, wherein theinsulating film is formed of an insulating film for planarization with abank layer formed thereon.
 7. The method for fabricating an organicelectroluminescent display according to claim 1, wherein the organicthin film layer is a hole transport layer.
 8. The method for fabricatingan organic electroluminescent display according to claim 7, wherein thehole transport layer is formed of PEDOT(Poly-3,4-Ethylenedioxythiophene) or PANI (polyaniline).
 9. The methodfor fabricating an organic electroluminescent display according to claim1, wherein a surface treated portion in the organic thin film becomesthe non-conductive and helps prevent leakage current to the lowerelectrode.
 10. The method of claim 1, wherein the another portion is aportion of the organic thin film layer which was not treated.
 11. Themethod of claim 2, wherein the another portion is a portion of theorganic thin film layer which corresponds to the lower electrode.
 12. Anorganic electroluminescent display comprising a lower electrode, a holetransport layer, a luminescent layer and an upper electrode sequentiallyformed on a substrate, wherein a portion corresponding to the lowerelectrode in the hole transport layer has surface characteristics and aresistance value different from a portion other than the portioncorresponding to the lower electrode.
 13. An organic electroluminescentdisplay comprising; a lower electrode formed on a substrate; aninsulating film formed on the substrate so that a portion of the lowerelectrode is exposed; an organic thin film layer formed on an exposedlower electrode and the insulating film; a luminescent layer formed on aportion of the organic thin film layer corresponding to the lowerelectrode; and an upper electrode formed on the substrate, wherein aportion of the organic thin film layer under the luminescent layer hassurface characteristics different from another portion of the organicthin film layer other than the portion under the luminescent layer. 14.The organic electroluminescent display according to claim 13, whereinthe organic thin film layer is a hole transport layer.
 15. The organicelectroluminescent display according to claim 14, wherein the holetransport layer is formed of PEDOT (Poly-3,4-Ethylenedioxythiophene) orPANI (polyaniline).
 16. The organic electroluminescent display accordingto claim 13, wherein the insulating film is a planarization film. 17.The organic electroluminescent display according to claim 13, whereinthe insulating film is a planarization film with a bank film is formedthereon.
 18. The organic electroluminescent display according to claim13, wherein the another portion of the organic thin film layer otherthan the portion under the luminescent layer, has an UV ray treatedportion and a higher resistance value than the portion under theluminescent layer, and the another portion of the organic thin filmlayer helps prevent leakage current between the organic thin film layerand the lower electrode.
 19. A method for fabricating an organicelectroluminescent display comprising the steps of: forming an organicthin film on a substrate; treating a portion of the organic thin filmwith UV rays while covering another portion of the organic thin film;and forming a luminescent of on the another portion of the organic thinfilm.